Location of objects has been solved in a number of ways for a number of purposes. One type that has been widely used is that referred to as the Vehicle Location System (VLS). This type of system utilizes a number of antennas, approximately three, that are disposed about a given location such as the city. Each vehicle is given a transceiver which is allowed to receive a location request signal, coded for a unique ID associated with the vehicle and then transmit a coded signal at a different frequency. The method of operation is to transmit the signal in a broadcast manner to all of the transceivers on all of the vehicles, the one recognizing its ID, then turning on and transmitting out in a broadcast manner a response having associated therewith the unique ID for that vehicle. A receiver associated with each of the antennas disposed about the location such as the city, then compares the time that the received signal was received at that location and compares it to a common time base. This is then transmitted back to a central station which utilizes a Time of Arrival location technique. This is basically a triangulation method. The problem with this type of system is throughput and the accuracy with which the time base must be maintained. Additionally, these systems must operate over very large areas and, therefore, must have relatively powerful transmitters.
In another type of system, the signpost system, vehicles are located by passing certain "signposts" that are disposed in a grid such as a network of rows in a city. By determining the various field strengths as the vehicle moves through the power field associated with a given signpost transmitter, and also receiving a unique ID from each of the signposts, the vehicle can determine certain information regarding the signpost and transmit it back to a central location that can determine the general location of the vehicle by determining which signpost it is close to. The main problem with prior art systems is that they have difficulty in making precise locations and also require virtually dedicated transmission links in order to maintain the transmission in order to provide the location. For example, in the Vehicle Location System, if the vehicle is moving, it is difficult to ever locate it as throughput allows the transceiver to only respond once to define the location. However, the request for location signal may have been sent out twenty minutes prior to sending out its location. If the vehicle is moving, then it may take another twenty minutes to find the next location of the vehicle.